Communication between components in the user space and the kernel space of an operating system is a known issue in datacenter management. This is especially a challenge for third-party software vendors who develop management software, drivers, modules, network interfaces, etc., for scalable computing platforms.
For example, in the area of cloud computing, host-management facilities are becoming critical architecture components as cloud deployments become increasingly scalable. In turn, the host-management facilities must also be scalable. The Common Information Model (CIM) architecture combined with host-inventory services allows an administrator to issue management operations from a single station to hosts and to have the operations serviced by vendor-specific CIM Provider software on each host. However, although the CIM architecture allows third-party developers to formally define the host-to-client interfaces supported by the CIM provider, the CIM architecture provides no guidance for defining the provider-to-kernel interface required to service the provider operations.
Further, in a virtualization platform, the primary method for third-party developers to implement user-space to kernel-space communication is through character devices. Character devices appear as file nodes in a file system and support traditional file operations (e.g., open, read, write, poll, ioctl, close, etc.). Kernel modules exporting character device interfaces register a series of file operations handlers. Thus, a user-space application performing a file operation on a file corresponding to the node in the file system triggers the character device interface.
One problem in working with character devices directly is a lack of structure and consistency in working with the low-level semantics. That is, many developers write their own (and often functionally equivalent or similar) interfaces ad hoc and implement common low-level transport operations and protocols (e.g., request decoding, parameter marshalling, and event delivery) to simply call a function inside kernel-space (or vice versa, to simply call a function inside user-space from the kernel-space). Typically, such interfaces require low-level bit manipulation and offer very limited methods of communication between kernel-space and user-space. In addition, because of the difficulty in programming low-level operations, the resulting application may be error-prone. Although it is possible to implement communications through file interfaces and socket interfaces, both approaches also have the fundamental constraint of being unable to send structured semantic data and operations across the user and kernel boundary. Like with character devices, using file interfaces and socket interfaces require that software on both sides pack and unpack the data.
Further, in the virtualization environment, because access to the kernel may be via the file system of the host computer, the applications that developers write to talk to the kernel are exposed to the file system. This limits portability for the management applications outside of the virtualization environment, which is already commonly constrained and may have little support for rich user applications. Also, complicated applications may use resources that can hinder the host computer's ability to efficiently run and manage virtual machines.
Additionally, the application programming interfaces (APIs) that third-party developers build on character devices (or even file interfaces and socket interfaces) lack inherent support for versioning, resulting in compatibility issues between user components and kernel components as time passes and later API versions are implemented. For example, a CIM provider from a particular third-party vendor may need to support multiple drivers, but the driver itself may evolve over time to add new features, such as after a firmware upgrade. In such a case, the CIM provider has no way to detect what high-level operations built on the low-level interfaces are supported. Current solutions are cumbersome and lead to breakage when a data structure definition changes even slightly. Presently, to prevent breakage and maintain compatibility, kernel- and user-space applications require tight integration and agreement.